1. Field of the Invention
The present invention relates to X-ray imaging apparatus; and more particularly to X-ray detectors which produce electrical image signal in such apparatus.
2. Description of the Related Art
Conventional X-ray imaging equipment includes a source for projecting a beam of X-rays through an object being imaged, such as a medical patient. The portion of the beam which passes through the patient impinges upon an X-ray detector which converts the X-rays attenuated by the patient into photons which then are converted into an electric image signal. One type of X-ray detector has a combination of a scintillator in front of a two dimensional array of photodetectors. Each photodetector integrates the energy of the impacting X-ray photons over the period of X-ray exposure time to produce a signal that is proportional to the X-ray energy integral or X-ray intensity. The electrical signal from each photodetector forms a picture element, commonly referred to as a pixel, which are processed and combined to form an image that is displayed on a video monitor. The resolution of the resultant X-ray image was adversely affected by the diversion, or spreading, of the light within the scintillator. In order to increase X-ray detection efficiency, it is desirable to increase the thickness of the scintillator, however increased thickness also increases the light spread.
U.S. Pat. No. 6,011,265 discloses a detector which can be used for X-rays or gamma rays. The radiation enters the detector through an inlet window and interacts with a gas to generate primary electrons. Those electrons pass through a cascaded series of gas electron multipliers (GEMs). Ultimately striking a linear set of charge collection electrodes. The charge collection electrodes are connected to read-out electronics which produce a pixel from the signal from each electrode.
The resolution of the resultant X-ray data is limited by the pitch, or spacing, of the charge collection electrodes. Thus, the ability to physically construct the electrode array and read-out electronics connected thereto, limits the resolution of the X-ray detector. Although advances in microelectronics enable formation of finer electrodes and denser electronic read-out circuitry to increase the image resolution, such increased resolution comes with a significant cost increase. Therefore, it is desirable to increase the X-ray image resolution without paying the price of increased density of the charge collection electrodes and electronics.